1. Field
The present disclosure is directed to a thermosetting oligomer or thermosetting polymer, a thermosetting resin composition including the thermosetting oligomer or thermosetting polymer, and a printed circuit board using the composition. More specifically, the thermosetting oligomer or thermosetting polymer has a low coefficient of thermal expansion and either a high or no glass transition temperature due to its thermal curability to achieve improved heat resistance, mechanical properties and dimensional stability.
2. Description of the Related Art
Recent advances in information and communication technologies have transformed our society into a high-tech communication and information society based on the convergence of computers and communication devices. The trend toward miniaturization and high performance of electronic devices, including mobile phones and personal computers, has led to high-density integration of printed circuit boards as essential elements of electronic devices. Such high-density integration is achieved by various methods, for example, by stacking printed circuit boards, reducing the thickness of printed circuit boards, and reducing the diameter and interval of through-holes. Accordingly, there is a need for novel printed circuit board materials with higher performance.
The use of high operating frequencies for rapid processing of data in electronic information devices such as computers involves problems of transmission loss and signal delay. In an effort to solve such problems, it is necessary to make use of copper clad laminates with a low dielectric constant and a low dielectric loss tangent. Generally, signal delay in a printed circuit board increases linearly with the square root of the relative permittivity of the insulating material surrounding interconnect lines. Thus, low dielectric constant resin compositions are needed to produce printed wiring boards that require high transmission rates.
Bismaleimide triazine (“BT”) resins and epoxy-based flame retardant 4 (“FR-4”) copper clad laminates that are currently in use as board materials suffer from the problems of severe transmission loss and signal delay because of their relatively high permittivity (ca. 4.5-5.5). Further, the board materials fail to provide other satisfactory properties, for example, comparable or improved mechanical properties, high heat resistance, low thermal expansion and low moisture absorption properties, which are required for effective subsequent packaging. Thus, there is a need for novel materials that meet the requirements for next-generation boards.
In this connection, research has recently been conducted on techniques associated with the use of liquid crystal polymer (“LCP”) resins. Thermoplastic liquid crystal polymers have attracted particular attention as potential replacements for polyimide (“PI”), which is currently used as a material for flexible copper clad laminates of flexible boards and rigid-flexible boards. The reason for this is that high moisture absorption, dimensional instability, high permittivity and high dielectric loss of polyimide can be solved by the use of thermoplastic liquid crystal polymers. Further, liquid crystal polymer resins have excellent electrical properties such as low permittivity and dielectric loss even at high frequencies (i.e., 1 gigahertz (“GHz”) or greater).
Liquid crystal polymers are may be used as materials for flexible and rigid-flexible boards and interlayer insulating materials, based on their excellent electrical properties (for example, very low permittivity and dielectric loss) and low coefficient of thermal expansion (“CTE”).
However, liquid crystal polymers, when used alone, exhibit low stiffness and insufficient heat resistance, making it difficult to use liquid crystal polymer in a semiconductor printed circuit board. For example, poor processability of meltable liquid crystal polymers can be problematic during production of a prepreg (i.e., a printed circuit board without laminated copper) for a printed circuit board or for lamination of copper foil on the prepreg. Soluble liquid crystal polymers have low glass transition temperatures (Tg), are processed at a high temperature, and are highly viscous because of solid components therein, which are disadvantageous in terms of impregnation efficiency. In addition, poor wettability of the soluble liquid crystal polymers on the surface of a copper foil makes it difficult to achieve high adhesive strength.